# 2008 Mercury Grand Marquis - Unexpected acceleration **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** mercury\ **Created:** [February 22, 2021, 4:50am UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358 "2021-02-22T04:50:49Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![farnak](https://avatars.discourse-cdn.com/v4/letter/f/d78d45/32.png) [@farnak](https://community.cartalk.com/u/farnak)\ **Post date:** [February 22, 2021, 4:50am UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/1 "2021-02-22T04:50:50Z")
unexpected car acceleration when slowing down ---
**Author:** ![VDCdriver](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/vdcdriver/32/30_2.png) [@VDCdriver](https://community.cartalk.com/u/VDCdriver)\ **Post date:** [February 22, 2021, 2:01pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/2 "2021-02-22T14:01:13Z")
What was your mechanic’s diagnosis? ---
**Author:** ![pyrolord314](https://avatars.discourse-cdn.com/v4/letter/p/6a8cbe/32.png) [@pyrolord314](https://community.cartalk.com/u/pyrolord314)\ **Post date:** [February 22, 2021, 2:18pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/3 "2021-02-22T14:18:19Z")
> [@farnak](#): > > unexpected car acceleration when slowing down were you wearing boots at the time and accidentally hit the accelerator instead of the brake? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [February 22, 2021, 3:37pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/4 "2021-02-22T15:37:58Z")
> **[Lawsuit: Older Fords can suddenly speed up](https://www.usatoday.com/story/money/cars/2013/03/28/ford-class-action-throttle-control-unintended-acceleration/2000861/)** > > Ford models needed a "fail safe" so the driver doesn't have to fill that role, lawyers say. Tester ---
**Author:** ![tcmichnorth](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tcmichnorth/32/25126_2.png) [@tcmichnorth](https://community.cartalk.com/u/tcmichnorth)\ **Post date:** [February 22, 2021, 3:56pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/5 "2021-02-22T15:56:33Z")
Dirty throttle body or faulty IAC can do this. ---
**Author:** ![bcohen2010](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@bcohen2010](https://community.cartalk.com/u/bcohen2010)\ **Post date:** [February 22, 2021, 3:59pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/6 "2021-02-22T15:59:16Z")
> [@pyrolord314](#): > > were you wearing boots at the time and accidentally hit the accelerator instead of the brake? Whenever someone claims that an unintended acceleration occurred, people always trot out this explanation, and the automakers themselves attempt to blame floor mats or careless drivers for the resulting accidents. However, there is a major hole in these excuses: these unintended acceleration events _almost always occur on vehicles equipped with a “drive by wire” throttle body._ **If floor mats or clumsy-footed drivers were to blame, then logically the problem would be just as prevalent on older cars with a physical connection from the accelerator pedal to the throttle body.** The fact that it’s almost _never_ a problem on the older design tells me that what most likely occurs–despite the automakers’ excuses and speculation–is that a worn spot in the accelerator pedal position sensor can result in “potentiometer noise” which tells the PCM that much more acceleration is desired than what the driver intends. If this scenario occurs, _there is no inherent safety like there would be with a traditional cabled throttle body._ If the throttle position sensor on a vehicle with a cabled throttle body fails in such a way as to specify rapid acceleration, while the driver is barely pressing (or not pressing) the accelerator, then the air/fuel mixture will become too rich, and the engine will stall. It won’t “run away” because the mostly closed throttle plate will prevent that. With drive-by-wire, the computer controls the amount of fuel _and_ air provided to the engine, so this won’t happen. Even a brake override feature in the PCM is a poor substitute for the inherent safety provided by the older design, but obviously much better than nothing. For this reason, I would only buy an older vehicle with a physical connection between the accelerator pedal and the throttle body. Newer is not always better, and sometimes it’s a lot worse. ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [February 22, 2021, 4:09pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/7 "2021-02-22T16:09:04Z")
"bcohen2010 Newer is not always better, and sometimes it’s a lot worse. Agree 100% new is not always better sometimes it is worse. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [February 22, 2021, 4:19pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/8 "2021-02-22T16:19:16Z")
Almost all cases are traced to driver error or jammed floor mats, sometimes stuck throttle bodies that needed cleaning. Eliminate those 3 possibilities first. ---
**Author:** ![pyrolord314](https://avatars.discourse-cdn.com/v4/letter/p/6a8cbe/32.png) [@pyrolord314](https://community.cartalk.com/u/pyrolord314)\ **Post date:** [February 22, 2021, 4:22pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/9 "2021-02-22T16:22:27Z")
> [@bcohen2010](#): > > Whenever someone claims that an unintended acceleration occurred, people always trot out this explanation I asked a question…didn’t say it explained the issue. When you have 13.5 feet like I do, this is a possibility to look into. > [@bcohen2010](#): > > the automakers themselves attempt to blame floor mats I think they did find that in some cases, the floor mats did get bunched up cause a problem > [@bcohen2010](#): > > Even a brake override feature in the PCM is a poor substitute for the inherent safety provided by the older design, but obviously much better than nothing. For this reason, I would only buy an older vehicle with a physical connection between the accelerator pedal and the throttle body. Newer is not always better, and sometimes it’s a lot worse. I think you’re worrying more about an extremely rare occurrence because of your fear of modern technology. I’ve never had this happen to me (despite my big feet 🙂 ) despite driving cars from the 80s-today. (also have never had my power windows fail, or my automatic locks go bad. The cylinder in my ignition in my Focus went bad, so my father-in-law and I jury rigged a push button start system instead! And that was still going no problems up until it met it’s demise. ---
**Author:** ![texases](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/texases/32/862_2.png) [@texases](https://community.cartalk.com/u/texases)\ **Post date:** [February 22, 2021, 4:34pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/10 "2021-02-22T16:34:22Z")
Looks like that Ford lawsuit was dismissed: > **[Ford Unintended Acceleration Class Action Lawsuit Dismissed](https://m.carcomplaints.com/news/2019/ford-unintended-acceleration-class-action-lawsuit.shtml)** > > A Ford unintended acceleration class action lawsuit is finally over after vehicle owners failed to provide evidence of defective electronic throttle control systems. ---
**Author:** ![wentwest](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/wentwest/32/6073_2.png) [@wentwest](https://community.cartalk.com/u/wentwest)\ **Post date:** [February 22, 2021, 5:19pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/11 "2021-02-22T17:19:59Z")
I agree, but there’s one other very important thing to add. I tell anyone that brings this issue up that you can always push the shift lever into N. There’s nothing to stop you, just whack it into N. No buttons, no levers, nothing. It will slide there easily. If you are worried about the engine “blowing up”, first of all are you more worried about the engine than you are about dying? Second, it won’t “blow up” because all the tech stuff that makes this runaway possible will keep the engine from over revving. So just put it in N, let it keep running so you have power steering and brakes, and coast to safety. When you are stopped completely, turn off the engine with the key. We make ZERO attempts to actually train people in how to handle emergencies in cars. It’s beyond stupid. ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [February 22, 2021, 5:32pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/12 "2021-02-22T17:32:26Z")
[quote="wentwest, We make ZERO attempts to actually train people in how to handle emergencies in cars. It’s beyond stupid. Agree I have also seen preventable accident’s by people forgettig to use the E brake and what the E stand’s for they seem to think it is a parking brake only. ---
**Author:** ![wentwest](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/wentwest/32/6073_2.png) [@wentwest](https://community.cartalk.com/u/wentwest)\ **Post date:** [February 22, 2021, 6:09pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/13 "2021-02-22T18:09:34Z")
We could go on and on about this. Instead people are carefully taught how to parallel park. How about how to survive a blown out tire. How to regain control of a car if you nod off and wake up on the grassy center divide. What to do if another vehicle hits your and you are still moving. How to survive aquaplaning. Lots of topics, and lots of people have been injured or died because no one ever took the time to help. ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [February 22, 2021, 6:16pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/14 "2021-02-22T18:16:01Z")
I agree with you 100% IMHO people are wanting the car to do it all for them I also thig that every time I see people making stupid mistakes that there should be a required driving course after they get two ticket’s. I blame cell phones for much of the stupidity I see on the road. ---
**Author:** ![Renegade](https://avatars.discourse-cdn.com/v4/letter/r/b4bc9f/32.png) [@Renegade](https://community.cartalk.com/u/Renegade)\ **Post date:** [February 22, 2021, 6:21pm UTC](https://community.cartalk.com/t/2008-mercury-grand-marquis-unexpected-acceleration/175358/15 "2021-02-22T18:21:22Z")
I don’t know how you feel about it but I think it is worse in town than it is on the open road.